There has been a strong demand for reduction of emissions of carbon dioxide in order to deal with atmospheric pollution and global warming. In the automobile industry, the reduction of emissions of carbon dioxide is highly expected in association with the spread of electric vehicles (EV) and hybrid electric vehicles (HEV). Thus, development of electric devices such as secondary batteries for driving motors as a key to practical application of such vehicles, is actively being carried out.
As for the secondary batteries for driving motors, lithium ion secondary batteries having high theoretical energy are gaining increasing attention, which is leading to rapid development of the lithium ion secondary batteries. The lithium ion secondary batteries generally include: positive electrodes obtained in a manner such that positive electrode slurry containing a positive electrode active material is applied to surfaces of current collectors, negative electrodes obtained in a manner such that negative electrode slurry containing a negative electrode active material is applied to surfaces of current collectors, and electrolyte layers interposed between these electrodes. The lithium ion secondary batteries have a constitution in which the positive electrodes, the negative electrodes and the electrolyte layers are housed in battery cases.
The lithium ion secondary batteries highly depend on the respective active materials used therein for improvement of capacity characteristics and output characteristics.
There is known a negative electrode material for a lithium ion secondary battery that achieves a high cycle property while keeping a high discharging capacity, as proposed in Patent Literature 1. The negative electrode material for a lithium ion secondary battery described in Patent Literature 1 includes several kinds of metallic components and carbon components containing fine carbon materials, and includes composite powder having a predetermined particle diameter.